Process for cracking propylene and isobutylene in the presence of hbr



Aprll 18, 1967 J HAPPEL ETAL 3,315,004

PROCESS FOR CRACKING PROPYLENE AND ISOBUTYLENE IN THE PRESENCE OF HBYFiled March 6, 1963 2 Sheets-Sheet 1 C 3 He CRACKI NG WITH HBR A DDITION a 35 LL] LD Q: (I) o w MAX I HBR m 0 us EV m E LU 25 o E C) Q 20 (3Lu 2 0: E :5

Lu J g n-fl Q 5 J E s 20 4O 6O 80 I00 0 MOLES CsHe DECOMPOSED) MOLE C3HeCHARGED JOHN HAPPEL CHARLES J. MARSEL IN VENiTOR 8 BY /fl M April 18,1967 J HAPPEL ETAL 3,315,004

PROCESS FOR CRACKING PROPYLENE AND ISOBUTYLENE IN THE PRESENCE OF HBrFiled March 6, 1965 2 Sheets-Sheet 2 O LLI (9 5 C4 H 8 CRACK ING WITH HBR ADDITION I I00 2 T v Q MAX.

5 HBR 9 USED 6O 8 E (I) [I 8 4o IE M NO 8 (2) HBR 3i O 5 c3 0 A 20 4O 6OI00 EL o 1 MOLES C4Hs DECOMPOSED W MOLE (34 H8 CHARGED JOHN HAPPELCHARLES J. MARSEL INVENTORS United States Patent Ofi 3,3l5,004 PatentedApr. 18, i967 lice 3,315,004 PROCESS; FOR CRACKING PROPYLENE AND IS@-BUTYLENE IN THE PRESE CE F Hlir John Happel, Hastings-on-Hudson, andCharles J. Marsel,

New York, NY, assignors to National Lead Company,

New York, N.Y., a corporation of New Jersey Filed Mar. 6, 1963, Ser. No.263,189 2 Claims. (Cl. 260-678) This invention relates to a novel andimproved catalytic thermal process for making mixtures of methylacetylene and allene from isobutylene and/ or propylene. In particular,the invention pertains to a process whereby isobutylene and/ orpropylene is cracked under special conditions in the presence of ahydrogen .bromide or hydrogen bromide itself to give improved yields ofthe desired methyl acetylene and allene.

It is well known that olefins such as isobutylene and propylene undergothermal decomposition or cracking when subjected to elevatedtemperatures in an inert atmosphere for prescribed periods of time. Itis also known that the cracking of isobutylene or propylene at ordinaryconditions results in relatively small yields or methyl acetylene andallene in the cracked products. In elforts to improve the yields of thedesired methyl acetylene and allene, it has been found necessary toconduct the cracking under special conditions of greatly reducedpressure as well as carefully controlled temperature and contact time.This method of operation has proved commercially unattractive mainlybecause of the inherent problems in obtaining reduced pressures at hightemperatures. These difliculties are especially severe in commercialoperations. Among these problems are the need for expensive equipment,problems in process control and poor heat transfer characteristics, allof which tend to be intensified when brought to commercial scaleoperations.

One of the more recently proposed methods of overcoming thedifl'iculties of the prior art processes is described in US. Patent No.2,763,703 issued to the present inventors on September 18, 1956. It isdisclosed therein that at temperatures Within the range of about 800 C.to 900 C. and at contact times ranging from 0.01 to 10 seconds, apreferred mixture of about 80 to 90 mole percent steam and 20 to 10 molepercent isobutylene, when cracked at atmospheric pressure yields up to 5mole percent conversion of isobutylene to methyl acetylene andsimultaneously an equal amount of allene in a single pass. The presentinventors have also shown that as an improvement thereover, attemperatures in the range of 1050 C. to 1150" C. and a contact time of0.001 to 0.06 second an identical mixture as above, of about 80 to 90mole percent steam and to 20 mole percent isobutylene, when cracked atatmospheric pressure gave up to 25 mole percent conversion toisobutylene to both methyl acetylene and allene in a single pass. Thisdata indicates that short contact times tend to increase the yield ofthe desired products. It was first revealed in this patent that goodyields of methyl acetylene and allene were obtained by crackingisobutylene though the cracking occurs at essentially one atmospheretotal pressure in the presence of an inert diluent. One atmosphere isthe most convenient pressure for commercial operation. A carefullycontrolled contact time was also found to be particularly important indetermining the products resulting from either of these two crackingprocesses. Prolonged contact time of the isobutylene feed in thecracking zone was found to cause breaking of the carbon chain of theisobutylene molecule to give predominantly carbon monoxide andacetylene. Prolonged contact time has also been found to result indecreased yields of methyl acetylene and allene since these products arecleaved by thermal decomposition. At the same time, however, it has beenfound necessary that the contact time be sufliciently long to allow forthe demethanization of the isobutylene molecule for production of thedesired methyl acetylene and allene. One Way to obtain this requiredclose control on contact time, is to cool rapidly the hot reactor exitgases to a point below which further significant thermal. decompositionwill occur. This rapid cooling operation has been termed shockquenching. It has also been disclosed that steam is a particularlyadvantageous diluent to use when cracking at an overall pressure of oneatmosphere or greater. This is true not only because of the fact thatsteam is an economical diluent and can readily be condensed out of theexit reactor gases, but also because steam suppresses the formation ofcoke and therefore decreases the loss of methyl acetylene and allene tothis worthless product.

There have been numerous elforts to develop commercially attractiveprocesses for the production of methyl acetylene and allene whichattempt to avoid the difficulties of the prior art processes and alsoyield greater amounts of the desired methyl acetylene and allene. US.Patent No. 2,925,451 issued to M. I. Hogsed on February 16, 1960,proposed converting isobutylene or propylene to methyl acetylene andallene by passage over a metallic filament of high resistivity, such asplatinum or Nichrome, heated to temperatures of at lea-st 900 C. Inaddition, the Hogsed process teaches use of a reaction pressure of lessthan 0.01 atmosphere. Improved yields of methyl acetylene and allene,especially allene are disclosed. One major disadvantage of the Hogsedprocess, however, is its lack of utility as a commercial operation. Thisis because of the necessity of operating under vacuum with all itsinherent disadvantages and also the fact that only small throughputs arepossible. The possibility that the hot Wire may act as a catalyst alsotends to make scaleup to commercial operation diflicult.

The basis of the present invention is the discovery that whenisobutylene or propylene is cracked in the presence of hydrogen bromideor a hydrogen bromide yielding compound, the presence of the hydrogenbromide acts to direct and improve the cracking in such a way so as toincrease the yield of the more valuable methyl acetylene and allene atthe expense of the less desirable by-products of the cracking process.It is the object of this invention to provide a catalytic crackingprocess for making methyl acetylene and allene from isobutylene or frompropylene which avoids the difliiculties of the prior art by operatingat essentially atmospheric pressure with short contact times using aninert diluent, preferably steam, and at the same time, by the additionof hydrogen bromide or a hydrogen bromide yielding compound, producingunexpected high yields of the desired methyl acetylene and allene. Thus,the disadvantages of each of the processes of the prior art are avoided.It has been found that, at high conversion levels, the presence ofhydrogen bromide or hydrogen bromide yielding compounds in the crackingprocess nearly doubles the yield of the desired products. It issurprising and unexpected that .such results can be obtained since inthe prior art some hydrocarbons including propylene have actually beensuggested as inert diluents for cracking other substrates in thepresence of hydrogen bromide.

Actual experimental data on the results of cracking propylene with andwithout the presence of hydrogen bromide are presented graphically inthe accompanying FIGURE 1 which shows the outstanding improvement inyield obtained by the catalyst addition. From actual operating dataobtained, a smooth curve has been drawn through the points in theaccompanying plot for the range of conversion. At high conversionlevels, the presence of hydrogen bromide in the cracking process morethan doubles the yield of desired products.

The term conversion in this specification is used to nean the ratio ofthe moles of propylene cracked to other )roducts per mole of propylenecharged to the reactor for a single pass. The term selectivity is usedto mean 'atio of the moles of C H hydrocarbons (methyl acetyene andallene) obtained per mole of propylene con- ;umed to other products fora single pass. The term yield as used in the specification means theratio of the moles of C H hydrocarbons formed per mole of propylene feedto the reactor. Used this way, yield is also equal to the product of theconversion multiplied by the selectivity. The accompanying graph ofactual experimental data is a plot of yield versus conversion.

It will be noted from the accompanying Figure 1 (curve 2) that yielddrops ofi rapidly for higher conversions when cracking without catalystaddition. For cracking with catalyst addition (curve 1), however, itwill be noted that yields steadily increase with conversion and reach amaximum at the very high conversion of about 85-90%, which is a highlydesirable result for commercial cracking operations.

A table (Table I) of actual experimental data is included hereinafter inthe examples, to describe more fully the improvement obtained byhydrogen bromide yielding compound addition in the cracking ofpropylene. It will be noted from this table that the selectivity of thedesired C H hydrocarbons obtained tends to increase with an increasingratio of hydrogen bromide to propylene in the feed to the reactor. Itwill also be noticed that the increased yields of methyl acetylene andallene are achieved at the expense of the less useful byproducts of thecracking, which is most desirable.

Actual experimental data from the cracking of isobutylene with andwithout the addition of hydrogen brornide are shown graphically in theaccompanying FIG- URE 2 and shows the outstanding improvement obtainedby the catalyst addition. For the actual operating data obtained, asmooth curve has been drawn through the points in the accompanying plotfor the range of conversions.

The accompanying FIGURE 2 of the actual experimental data is a plot ofyield versus conversion. It will be noted from the accompanying graph(curve 2) that the yield drops off rapidly for higher conversions whencracking without catalyst addition. For cracking with hydrogen bromide(curve 1) addition, however, it will be noticed that yields steadilyincrease with conversion and reach a maximum at the very high conversionof about 80-85%, which is a highly desirable result for commercialoperation. This a very unexpected and unpredictable result usinghydrogen bromide or hydrogen bromide producing compounds, i.e., HBrforming at the conditions and with the materials in the cracking zone.It will be noticed from the accompanying table (Table 2) that theselectivity of the desired C H hydrocarbons obtained tends to increasewith an increasing ratio of hydrogen bromide to isobutylene in the feedto the reactor. It will also be noticed that the increased yields ofmethyl acetylene and allene are achieved at the expense of the lessusetul byproducts of the cracking which is, of course, most desirable.

It has been found that improvements in yields of desired product areobtained from about 5 moles of HBr per 100 moles of olefin, and thatyields tend to increase steadily up to ratios of over 60 moles of HBrper 100 moles of olefin. In carrying out the process, the reaction zonecontact time should be within the range of 0.0005 to 0.06 second, whilethe mole percentage of steam to olefin feed may be varied between 40 and95 percent. The preferred contact times are in the range of 0.001 to0.005 seconds. Reaction pressures for the isobutylene will vary fromabout 0.05 to 0.30 atmospheres or about 38 to 225 mm. Hg by dilution andtotal pressure may be kept conveniently at one atmosphere. The molarratio of hydrogen bromide to isobutylene may be varied from as low asrequired depending on the aims of the process up to a maximum which isdictated by economics. The lower practical limit of hydrogen bromide toisobutylene was found to be about 5 moles of HBr per 100 moles of olefinfeed, a point at which significant improvements in yield 5 over thatobtained without HBr addition becomes apparent. The optimum ratio ofH131 to feed is governed generally by the economics of the particularprocess and will be determined by a balance between the cost of hydrogenbromide recovery and recycle and the savings in plant and operating costobtained by the increased yields of methl acetylene and allene due tohydrogen bromide addition.

The preferred method of operation for propylene is from a mole ratio ofsuperheated steam to propylene and propylene to hydrogen bromide of to 1and 1 to 1 moles respectively, up to a mole ratio of superheated steamto propylene and propylene to hydrogen bromide of 4 to l and to 1 molesrespectively. The preferred contact time is from 0.0005 second to 0.01second. The effective temperature in the cracking zone is above 900 C.and ranges from 800 C. to 1250 C. The maximum yield of methyl acetyleneand allene is obtained at conversions of 70 to 90 percent of the feed.

The preferred method of operation for isobutylene is from a mole ratioof superheated steam to isobutylene and isobutylene to hydrogen bromideof 10 to 1 and 1 to 1 moles respectively up to a mole ratio ofsuperheated steam to isobutylene and isobutylene to hydrogen bromide of4 to 1 and 15 to 1 moles respectively. The effective temperature rangein the cracking zone is from 700 C. to 1150 C. At a temperature of about800 C., the conversion is low (below 10%). At temperatures of about 1000C., the conversion is high (above 90%) but the selectivity falls off. Itappears that using the above defined reaction conditions, the maximumyield of methyl acetylene and allene is obtained at conversions of 80 to90 percent.

Concerning the method of carrying out this invention, various methods ofachieving the required reaction temperatures may be employed and anumber of such methods are illustrated below. It is not intended,however, to limit the invention in any way to any particular method forcarrying out the process.

(1) A hot gaseous stream of superheated steam is added to the olefinfeed stream, or

(2) The olefin feed stream is passed quickly through an electric arczone, or

(3) A portion of the olefin gas stream is burned and provides hotcombustion gases, which heat up the main feed stream to the desiredtemperature range, or

(4) Powdered particles of an inert material, e.g., alumina are heated atelevated temperatures and injected into the olefin feed stream.

A particularly advantageous method of achieving the high temperaturesfor cracking with good control is to mix the olefin feed withsuperheated steam just prior to its entry into the cracking section. Therapid mixing and dififusion of the two gases because of high velocityand high temperature will very rapidly bring the feed to the desiredcracking temperature. It is also advantageous to preheat the olefin feedjust prior to mixing in order to conserve on the temperature and use ofthe superheated steam, but it is not a necessity for the invention thatthis preheating of the olefin feed occur. It is necessary, however, thatthe superheated steam entering or admixed be at a temperature greaterthan that in the cracking zone since it will essentially determine thefinal temperature of the olefin, steam, and hydrogen bromide or hydrogenbromide yielding compounds, admixture entering the re actor.Anotheradvantage of steam dilution is the fact that the cracking ofisobutylene or propylene to methyl acetylene and allene is anendothermic reaction and thus heat is absorbed during the crackingresulting in a temperature drop within the reaction zone. The hightemperature steam dilution acts as a heat source to keep the crackingzone at a more constant temperature and provide more accurate control ofcontact time. The high temperature steam necessary for this purpose canvary in temperature from 1000 C. to 2000 C. as required and thistemperature may be obtained in a variety of Ways, among them being theuse of a high temperature pebble heater, the mixing of low temperaturesteam with the very hot steam product from the burning of hydrogen andoxygen to give the desired high temperature steam or the use ofelectrical heating. The superheated steam diluent need not be sure, butmay also be mixed with gases obtained by the combustion of a fuel.desirable, however, that the steam 1 since this will allow forsubstantially tion of the diluent from the cracked gases. This willreduce the problem of purifying these cracked gases since they enter thepurification system undiluted by the extraneous gases of the dilutionsteam mixture. Therefore, by using relatively pure dilution steam, thecracked gases reach the purification system at their maximumconcentration for the most etficient recovery of the desired methylacetylene and allene. The additional advantage of using steam dilutionto prevent coke formation is also of value.

Careful control of contact time is necessary in order to obtain therequired conditions of this process. Contact time is defined as thevolume of the reaction zone divided by the volume of feed at thereaction temperature. As previously mentioned, the cracking is anendothermic reaction and there is a varying temperature profilethroughout the length of the reactor. Therefore, the proper integratedeffective temperature must be used in order to determine the volume ofthe gaseous feed through the reaction zone. The contact time may bevaried by varying the rate of gases going through the reactor. Variationof temperature will also vary contact time by changing the volume of thefeed through the reaction zone. Contact time can also vary for a givenfixed feed by replacement with reactors of various volumes or using aseries of reactors with fixed cross section but with varying lengths.Rapid termination of contact time is best obtained by direct contactwith a deluge of water or oil. It is also possible to contact thereaction zone gases with cool gases or powdered, inert material such asalumina, the method of cooling being unimportant so long as the exitreactor gases are cooled very quickly to below at least 500 C. Thisrapid cooling serves to prevent thermal decomposition of reactionproducts, prevent polymerization and to control contact time.

The hydrogen bromide additive of this invention may be added in manyforms, as a liquid or vapor depending on the compound and the pressure.It is also possible to use an organic or mineral compound containingbromine which under the cracking conditions in the reactor decomposes toyield required amounts of a bromide of the form such that it isrecovered as hydrogen bromide. mineral compound is used which liberateshydrogen bromide under the conditions in the reactor, it is convenientto dissolve it in water which is subsequently converted to steam andthen acts as the inert diluent for cracking.

Representative of organic bromine compounds which may be used in thereaction are ethyl bromide, 2 bromopropane, l-bromobutane, and the like.Mineral bromine compounds which may be used in the process of theinvention are hydrobromic acid and water soluble bromine compounds.Suitable compounds in the scope of the invention must decompose ordissociate under the conditions of the reaction to form hydrogenbromide. An economic method of introducing a hydrogen bromide yieldingcompound is to use HBr as the reagent. The mixture of HBr and steamafter passing through the cracking zone is readily recovered in thequench system. If the exit gases from the cracking reactor are quenchedwith water, a dilute solution of the HBr originally fed is obtained. Ifthe exit gases are quenched with another material such as an oil, theHBr dissolves in the condensed steam. Recovery of the HBr for reuse inthe cracking zone may be accomplished by distillation, absorption or anyother well known means.

This invention may be carried out with pure isobutylene or purepropylene or with a commercial fraction containing these compounds suchas is obtained by distillation or extraction in a petroleum operation orthe like.

The invention Will be more fully understood by reference to thefollowing illustrative examples of the preferred methods of operation,however, these examples are for illustration only and are intended in noway to limit the invention specifically thereto.

Example 1 A propylene feed stream is metered and intimately mixed withsuperheated steam and HBr just before introduction into a 9" longschedule stainless steel reactor. The mole ratio of steam to propyleneis kept at about 6.7 to 1. The temperature in the center of the reactoris about 1015 C, and the contact time is 0.00207 second. The resultingpropylene conversion is 55.6% and selectivity of allene and methylacetylene obtained is 23.6% as determined by exit gas analysis. Whilethese flows are held constant, HBr is added at a molar ratio of 0.078mole of HBr per mole of propylene. The temperature is determined to be1028 C. The resulting conversion is 56.3% and the selectivity of methylacetylene and allene is 34.3% as determined by exit gas analysis. TheHBr mole ratio is then increased to 0.117 mole of HBr per mole ofpropylene. The temperature is 1030 C. as read by a thermocouple.Conversion is 56.9% and selectivity is 39.1% as determined by exit gasanalysis. The HBr is then increased to 0.526 mole of HBr per mole ofpropylene, and temperature is determined to be 1020 C. The conversion is52.9% and selectivity is 50.4% as determined by exit gas analysis. Thisseries of runs clearly discloses the great improvement obtained by HBraddition into the cracking zone.

Analytical results of the 0.526 HBr to after making allowances forburner gas and other sources propylene run, excess hydrogen from the isgiven below:

Component: Mole percent H 29.50 0 0.77 N 0.92 CH 14.71 (1 H 6.15 (:00.47 C H 0.03 0 H, 25.58 C H 7.14 Allene 5.41 Methyl acetylene 9.10 H0.23

Example 2 A propylene feed stream is metered before being introducedinto an experimental inconel cracking tube which is one-half inchschedule 80 and 11 inches long. Measured quantities of superheated steamand hydrogen bromide are then intimately mixed with propylene just priorto the reactor tube entrance. The superheated steam which has beenpreviously heated in a zone where hydrogen-oxygen combustion is takingplace, is passed into the reactor. The mole ratio of steam to propyleneis 6.7 to 1. The total reactor pressure is kept at about one atmosphereduring the reaction and a thermocouple in the middle of the crackingtube registers a temperature of 1080 C. The contact time of reaction asdetermined by the effective temperature is about 0.0036 second and theresulting conversion is 56.8%. A water quench is used immediatelyfollowing the reaction zone and after steam condensation and waterremoval, the effluent gas is analyzed. From this data selectivity isdetermined to 6 31.9% for methyl acetylene and allene. While these owsare held constant, HBr is introduced at a molar atio of 0.078 mole ofHBr per mole of propylene. The :mperature is determined to be 1100 C.The resulting 8 selectivity was determined to be 73.4 percent. Analysisof the reaction products was obtained after making allowances for theexcess hydrogen from the burner gas and for other gases which wereobtained from sources onversion is 52.7% and the selectivity of methylacetyl- 5 other than the cracking reaction and the analytical results neand allene are determined to be 32.3%. The HBr are given below.

T role ratio is then 1ncreased to 0.117 mole of 1-IBr per Component:M01e percent nole of propylene. The temperature is 1085 C. and theHydrogen 7 17 onversion is 51.6%. The selectivity as determined byOxygen n 2 47 xit gas analysis is 42.8%. Again the HBr mole ratio 10Nitronen' n 035 s increased to 0.526 mole HBr per mole of propylene, andMethgne 4O 88 he conversion is 52.0%. The selectivity as determined by"7 u 8 n31 dt 47 Canbon monoxide 2.1 an gas a ysrs agar 1 crease o 0.Ethane 010 Example 3 1r Ethylene 1.73 9 7 The data In the followingTable I was obtained using g dloxlde 2 different size reactors as soindicated in the table. The 1 effect of intermediate quantities ofhydrogen bromide are g i shown. Conditions are used and results obtainedas e Allene 11.59 OWIl.

TABLE I.THERMAL CRACKING OF PROPYLENE Percent Selectivity X- ExperimentM0195 Percent gigs; Tempera- Contact Number HBIXIOO Converture, C. Time,(31H4 C3115 S1011 C3114 021*14 CzHg C3115 SGCOlldS 0 55. G 23. 6 42.229.4 6. 7 1, 015 2. 07 13.11 7. 3 56. 3 34. 3 34. 5 27.1 6. 7 1, 023 2.03 19. 34 11.7 56.9 39.1 29.3 25.9 6. 7 1, 030 2. 01 22. 26 52. 6 52.950. 4 21. 4 24. 3 6. 7 1, 020 1. 92 26. 66 0 96. 4 6. 3 20.7 55.1 6. 71,190 1. 32 6. 07 7. 3 97. 7 3. 0 15.6 60. 3 6. 7 1, 200 1. 79 7. 7911.7 95.1 9. 3 13. 3 66. 3 6. 7 1, 200 1. 73 9.12 52.6 93. 7 11.7 9. 069. 2 6. 7 1,130 1. 71 11.55 0 34. 5 19.1 33.1 44. 0 6. 7 1,075 2. 0116.14 7. 3 35.4 20. 3 26. 3 44. 7 6. 7 1,085 1. 93 17. 76 11.7 36. 5 23.3 23. 4 45. 6 6. 7 1, 035 1. 96 20.59 52.6 34. 6 36. 5 17.3 43. 0 6. 71, 075 1. 37 30. 33 0 7.1 23.2 30.5 4.3 6.7 830 3.53 1.65 7. 3 5. 5 23.7 24. 9 1. 2 6. 7 335 3. 47 1. 11.7 6. 6 30. 3 31. 5 3. 4 6. 7 330 3. 472.00 52. 6 5. 6 37. 9 25. 6 3.3 6. 7 325 3. 31 2.12 0 35.0 23.3 43. 720.3 6. 7 965 3. 22 9. 91 7. 3 37.9 33. 7 37.1 13. 5 6. 7 930 3.15 14.67 11.7 35.1 44. 6 32.1 13. 5 6. 7 975 3.15 15. 65 52.6 31. 5 54. 3 22.3 17.3 6. 7 955 3. 03 17.10 0 14. 9 23. 3 35.3 s. 0 6. 7 360 3. 63 5.737. 3 15.4 39. 2 40. 2 9. 2 6. 7 335 3. 53 6. 04 11.7 15.1 42. 2 37.3 9.5 6. 7 330 3. 27 6. 39 52.6 11.9 52.3 29. 4 9. 5 6. 7 330 3. 09 6. 22

The above runs were made in a 9 long stainless tube Schedule 80 Theabove runs were made in an 11 long Ineonel tube Schedule 80 Example 4Isobutylene 12.09 An 1sobutylene feed stream 1s metered and then pre-Methyl acetylene 1440 heated before being lntroduced 111110 anexperimental 55 Butadiene 090 stainless steel cracking tube which 1sone-half 1nch Sched- A tile 80 and is 9 inches long. Measured quantitiesof Total 9999 superheated steam and hydrogen bromide are then intimatelymixed with the isobutylene just prior to the E l 5 reactor tubeentrance. The superheated steam which has been previously heated in :azone where hydrogen-oxygen combustion is taking place, is passed intothe reactor. The mole ratio of steam to isobutylene and isobutylene tohydrogen bromide are 9 to 1, and 1.57 to 1 respectively. The totalreactor pressure is kept at about one atmosphere during the reaction anda thremocouple in the mid- \dlfi of the cracking tube registers atemperature of 995 C. and the exit temperature from the pyrolysis tubeis 902 C. The isobutylene is added after being preheated to atemperature of 200 C. The contact time of reaction as determined by theeffective temperature is about 0.0015 second and the resultingisobutylene conversion is 74.6 percent. A water quench is usedimmediately following the reaction zone and after steam condensation andwater removal, the efiluent gas is analyzed. From this data,

An isobutylene feed stream is metered and then preheated before beingintroduced into a stainless steel tube of the same dimensions aspreviously .given in Example 4 above. Measured quantities of superheatedsteam and isobutylene are intimately mixed just prior to the reactortube entrance. The mole ratio of steam to isobutylene is 10 to 1. Thetemperature in the reactor tube is about 1020 C. The contact time isdetermined to about .0013 second. The resulting isob-utylene conversionis 80.2 percent and selectivity for methyl acetylene and allene is 38.6percent 138 determined by analysis of the exit gas. While these flowsare kept essentially constant, HBr is added at a molar ratio of 11.8moles of isobiutylene feed to 1 mole of HBr. The temperature isdetermined to 75 be about 1020 C. The resulting conversion is 85.8percent and selectivity rose to 46.4 percent as determined by effect ofintermediate quantities of hydroben bromide analysis of the exit reactorgas. The ratio of HBr to are shown. Conditions were used and resultsobtained isobutylene is then increased to 7.55 moles of isobutylene asshown.

TABLE IL-TI-IERMAL CRACKING OF ISOBUIYLENE M Mole Percent SelectivityMole Reactor Experiment Ratio Percent Ratio Contact Temp, Number HBr 10Conversion Steam Time, 0.

180 X a 2 z z ISO Sets.

Using a 9 long one-half inch Schedule 80 stainless tube 0 22.1 05. 4 5.17. 3 10 0. 0017 935 47. 0 35. 5 79. 5 3. 7 4. 5 0. 0010 930 0 55.7 51.811.8 18.8 10 0 0015 985 54. 0 74. 5 73.4 4.9 10.9 10 0 0015 995 45. 775. 0 69.1 5. 2 12.4 10 0 0010 1, 000 07.9 75.0 71.2 5.8 12. 5 10 0 0015990 0 80.2 38.6 10.0 30. 7 10 0 0013 1, 020 7.8 85.8 40. 4 11.4 32.4 100 0013 1,020 11.7 82. 8 51. 4 12. 7 31. 4 10 0. 0013 5 52. 5 04. 1 55. 55. 3 24. 9 10 0. 0013 1, 020 For an 11 Ineonel reactor of the samediameter as previously given M 0 22. 4 05. 3 8. 1 10. 9 10 0. 0033 9757. 7 27. 8 72. 2 5. 3 7. 5 10 0. 0033 945 11.0 31. 9 73. 3 4. 9 5. 4 100. 0033 950 52. 0 35. 6 80. 5 5. 5 4. 0 10 0. 0033 955 to 1 mole of HBr.Analysis of the exit gas revealed that What is claimed is: a conversionof 82.8 percent and selectivity of 51.4 per- 1. A process for preparingallene and methyl acetylene cent is obtained. And again, the ratio ofHBr to isofrom propylene which comprises subjecting a mixture ofbutylene is increased to 0.9 moles of isobutylene per propylene andhydrogen bromide or a bromide containmole of HBr. Analysis of the exitgas revealed that a ing material capable of yielding hydrogen bromide atconversion of 94.1 percent and a selectivity of methyl the reactionconditions, the mole ratio of propylene to acetylene and allene of 55.5percent is obtained. This hydrogen bromide being from 1 to 1 to 15 to 1,to a temseries of runs very clearly points up the improvement obperatureof above 900 C. for from about 0.0005 to 0.01 tained by HBr additioninto the cracking zone. second and under conditions such that about 70to 90 percent of the propylene is converted, and separating al- Example6 I lene and methyl acetylene from the resulting product. lwbiutylenefeed stream 18 mete/176d and then P 2. A process for preparing alleneand methyl acetylene heated before being introduced into 11 inch, FF-from isobutylene which comprises subjecting a mixture of inch SChClUlInconel tube. Measured quant1t1es 0f i obutylene and hydrogen bromide ora bromine containsuperheated Steam and iwblltylene feed are intimatelying material capable of yielding hydrogen bromide at the mixed justprior to the reactor tube entrance. The mole reaction conditions, themole ratio of isobutylene to hyratio of steam to isobutylene is 10 to 1.The temperature drogen bromide being from 1 to 1 to 15 to 1 t a t in thereactor tube is about 975 C. Th C nta t t m perature of above 700 C. forfrom about 0.0005 to 0.06 is determined to be about .0033 Sec nd- Tresulting second, and under conditions such that about 80 to 90isobutylene col'lvelrsioll is Percent and selectivity of percent of theisobutylene is converted and separating al methyl acetylene and alleneis 66.3 percent as determined l d h l acetylene f the res by analysis ofthe exit gases. While these flows are kept essentially constant, HBr isadded at a molar ratio of ulting product.

11.8 moles of isobutylene feed to 1 mole of HBr. The References Cited bythe Examiner tempenature is determined to be about 960 C. The re- UNITEDATES PATENTS suiting conversion is 27.8 percent and the selectivity in-2,370,513 2/1945 A t 1 26() 63() creases to 72.2 percent as determinedby analysis f t 2,397,638 4/1946 Bell et al 260-683 exit gases. Theratio of HBr to isobutylene is increase-d 2,429,555 10/1947 Rice 260-478to 7.55 moles of isobutylene to 1 mole of HBr. Analysis 2 763,703 9/1956 Happel et 1 260 678 of the exit gas reveals that a conversion of31.9 pe ce 2,925,451 2/1960 Hogsed 2.60- 678 and a selectivity of 73.30percent is Obt in T ratio 3,082,273 3/1963 Peer et al 260678 of HBr toisobutylene is increased to 0.9 moles f i 3,207,806 9/1965 Baj-ars 26068O butylene per mole of HBr. Analysis of the exit gas revealed that aconversion of 35.6 percent and selectivity FOREIGN PATENTS of 305percent is Obtaineci 807,149 1/1959 Great Britain.

E I 7 868,566 5/1961 Great Britain. 915,447 1/1953 Great Britain. Thedata in the following Table II was obtained using different sizereactors as indicated in the table. The P AUL COUGHLAN, PrimaryExaminer-

1. A PROCESS FOR PREPARING ALLENE AND METHYL ACETYLENE FROM PROPYLENE WHICH COMPRISES SUBJECTING A MIXTURE OF PROPYLENE AND HYDROGEN BROMIDE OR A BROMIDE CONTAINING MATERIAL CAPABLE OF YIELDING HYDROGEN BROMIDE AT THE REACTION CONDITIONS, THE MOL RATIO OF PROPYLENE TO HYDROGEN BROMIDE BEING FROM 1 TO 1 TO 15 TO 1, TO A TEMPERATURE OF ABOVE 900*C. FOR FROM ABOUT 0.0005 TO 0.01 SECOND AND UNDER CONDITIONS SUCH THAT ABOUT 70 TO 90 PERCENT OF THE PROPYLENE IS CONVERTEDC, AND SEPARATING ALLENE AND METHYL ACETYLENE FROM THE RESULTING PRODUCT.
 2. A PROCESS FOR PREPARING ALLENE ANDMETHYL ACETYLENE FROM ISOBUTYLENE WHICH COMPRISES SUBJECTING A MIXTURE OF ISOBUTYLENE AND HYDROGEN BROMIDE OR A BROMINE CONTAINING MATERIAL CAPABLE OF YIELDING A HYDROGEN BROMIDE AT THE REACTION CONDITIONS, THE MOLE RATIO F ISOBUTYLENE TO HYDROGEN BROMIDE BEING FROM 1 TO 1 TO 15 TO 1, TO A TEMPERATURE OF ABOVE 700*C. FOR FROM ABOUT 0.0005 TO 0.06 SECOND, AND UNDER CONDITIONS SUCH THAT ABOUT 80 TO 90 PERCENT OF THE IOSBUTYLENE IS CONVERTED AND SEPARATING ALLENE AND METHYL ACETYLENE FROM THE RESULTING PRODUCT. 